This study presents a new green technology for the sustainable utilization of carbon dioxide. Synthetic methane, if produced effi ciently and with low carbon footprint, provides a ready replacement for natural gas in the existing energy, manufacturing, and transportation industries. The fi rst technology for the production of methane from CO 2 and water by molten electrolysis is demonstrated. The technology is more effi cient than alternative renewable methane production by microbial, aqueous, or solid oxide electrolysis, or than various photocatalytic processes. Methane is produced at 1000-fold the rate observed in photoelectrochemical systems, and without noble metals or an external hydrogen source. Added steam and CO 2 continuously renew the electrolyte. CO 2 and H 2 O are directly transformed by electrolysis at 97.4% current effi ciency at a constant current of 250 mA through 20 cm 2 iron and nickel electrodes in a 600 °C alkali carbonate/LiOH electrolyte at low (<2 V) energy. The electrolysis product is comprised of 64.9% methane, 34.8% H 2 , and 0.3% longer (than C1) hydrocarbons.
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